Far be it from us to tell Mike Bloomberg how to spend his money. But you’d think a successful businessman would have a better feel for his customers.

Bloomberg is pushing his line on guns in the Illinois primary for the congressional seat vacated by the now-disgraced Jesse Jackson Jr. The mayor’s Super PAC has contributed $2.1 million to the effort, mostly to run ads blasting Debbie Halvorson, a former House member who has been skeptical of a ban on assault weapons.

Halvorson accuses Bloomberg of trying to “buy” the election. Illinois Gov. Pat Quinn says the same: “We should not allow anyone with huge amounts of money to dictate the terms of the political debate.”

Hey, it’s a free country. But Bloomberg would do better by going with what is surely the most attractive product he has to offer Chicagoans: his own successful approach to crime.

Last year, Chicago had 506 murders — versus New York’s 419 — despite a population a third the size. In January, Chicago had three times the homicides (42 vs. 14). Rahm Emanuel’s approval ratings have plummeted as he gains a national reputation as the Mayor of Murderville.

Yet, thus far Emanuel has been reluctant to learn from Bloomberg on crime.

Seems to us that Second City residents would welcome an outsider who could change the terms of that political debate.